1. Field of the Invention
This invention relates an optical disk device for performing read and write of data for an optical disk such as a CD, MD or DVD, and particularly to control of track jump of moving a pick-up head to a target track formed on the recording face of an optical disk.
2. Description of the Related Art
Traditionally, there has been an optical disk for reading the data recorded on the optical disk such as a CD, MD, DVD, etc. and writing data in the optical disk. The optical disk includes a plurality of concentric or spiral tracks formed on the recording face. The optical disk device reads data recorded on the track by detecting the reflected light of an light beam projected on the track. Further, the optical disk device writes data in the track by irradiating the light beam.
Where the data recorded on the track is to be read or the data is to be recorded in the optical disk, in some cases, the optical disk device performs track jump to move a pick-up head to a target track. The target track refers to a track for which the read or write of data is performed. The track jump refers to an operation of moving the irradiating position of an light beam in a radial direction of the optical disk to locate the position on the target track. For example, JP-A-10-320938 discloses conventional control of the operation relative to track jump in the optical disk device.
The pick-up head is placed on a thread which is movable in the radial direction of the optical disk. The thread is adapted to be movable in the radial direction of the optical disk by a thread motor (hereinafter simply referred to as a motor).
The lens of the pick-up head is adapted to be movable for the thread. The lens is adapted to be movable in the radial direction of the optical disk by an actuator.
The track jump includes the cases of moving the thread and not moving the thread. Now, the track jump of moving the thread will be explained below.
First, a kick signal (the kick signal which is first given at the start of track jump is referred to a driving kick signal) is applied to a motor to start the movement of the thread. The driving kick signal is given with a prescribed magnitude and for a prescribed time. After the driving kick signal has been stopped, the kick signal (hereinafter referred to as an accelerating kick or decelerating kick) having a magnitude corresponding to the moving speed of the thread is applied to perform the constant speed control of moving the thread toward the target track at a constant speed.
The constant speed control employs the wavelength (period) of a tracking error signal described later. Further, after a lapse of a prescribed time from when the driving kick signal is applied to the motor, the kick signal is applied to the actuator so that the moving control of the lens of the thread and actuator is started.
The irradiating position of the light beam successively traverses the tracks formed on the recording face of the optical disk. A mirror section which totally reflects the light beam is formed between the adjacent tracks. On the basis of the amount of light reflected from the optical disk, a sinusoidal tracking error signal (TE signal) is obtained which represents that the lens center traversed the track. The tracking error signal is created by a wavelength whenever the lens center traverses the track. Therefore, by counting the number of the waves of the tracking error signal, the number of the tracks which the lens center has traversed is obtained. Further, on the basis of the wavelength (period) of the tracking error signal, the moving speed of the lens relative to the optical disk is obtained.
Immediately before starting the track jump, the optical disk device computes the number of tracks over which the lens center must move to reach the target track. Concretely, the number of tracks to move is computed on the basis of a difference between the track address representative of the present track position and that representative of the target track position.
When the lens center approaches the target track to a certain degree, the optical disk device brakes the motor to stop the thread beforehand. For example, when the lens center reaches the track located 100 tracks before the target track, the thread is stopped. Thus, the pick-up head body moves to the vicinity of the target track.
In this case, the optical disk device does not stop the movement of the lens by the actuator, but continues the movement of the lens toward the target track. When the optical disk device judges that the lens center has reached the target track on the basis of the counted number of waves of the tracking error signal, it causes the lens center to track on the target track by tracking servo.
Meanwhile, when the driving kick signal is simultaneously applied to the thread and actuator, since the thread has poorer response than that of the actuator, the actuator starts to move before the thread starts to move. Therefore, the thread and the actuator move separately so that the subsequent control cannot be carried out appropriately. This presents a problem of greatly vibrating the lens and others. In such a case, there is strong possibility of the track jump ending in failure. In order to obviate such an inconvenience, a method has been proposed which applies the driving kick signal to the actuator after a lapse of a prescribed time after the driving kick signal has been applied to the thread as described above.
However, the time taken from when the driving kick signal is applied to the motor to when the thread starts to move is affected by the friction force generated when the thread is moved. The friction force varies according to the elements which constitute the thread. Therefore, the conventional method which applies the kick signal to the actuator after a lapse of a prescribed time provides some devices in which the thread has already moved excessively and some devices in which the thread does not almost move (there are unevenness among the devices). Thus, in order to control the thread and actuator in good balance, the above prescribed time from when the driving kick signal is applied to the motor to when the kick signal is applied to the actuator must be set for each device. This presents a problem of complicating the process of manufacturing the device body and hence cost-up.